Mortar VS Furnace - Which is the better four elixir building?

I've been using furnace for a while now, as it's my go to building and provide some solid support and, in some instances, tower damage. Well before that, I used mortar decks, mainly in an offensive posture.

Now in challenges, I'm seeing some luck placing mortar as if it were a Furnace. This way, it does damage to troops before they even make their way over, as well as provides sports for attacks.

There's also the added advantage of it being a common, and therefore easier to level up, without having to worry about what towers it's going up against

Objectively speaking, which is the better building? I may make my way back to the mortar, especially with this new balance update.